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Old 06-03-2012, 02:07 PM   #11
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Originally Posted by ronhanson View Post
Standard since at least 2009 is a Generac. Onan is an upgrade.

Ooh! Didn't know that!
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Old 06-03-2012, 02:08 PM   #12
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I just looked at my manual and it looks very simple to replace the brushes. The only question I have is the + and the - wires in a plug or seperate? Just thinking what else could have been changed.

Was the original set of brushes burnt the same way?
It's AC. Doesn't matter.
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Old 06-04-2012, 11:16 PM   #13
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I replaced the generator brush block 150 hours ago, and today when I went to do my monthly run, no run and trouble code 341.

Took the brushes out, and the top brush was down to nothing again! The top slip ring was nasty looking, as well.

I burnished the slip ring with some #200 emery cloth on a stick, replaced the bad brush with the one that I had saved from the original fuse block, and we'll see what happens! I still have three months of warranty left, so I'm going to be watching this closely!

I hate to take it back to the dealer and wait a month during the high season, but you gotta do what you gotta do!
I would notify dealer, take photos of two failed brushes. You make it sound as though its the same brush each time. If so that normally means the excitor feeding this brush for excitation of the and/or field poles is shorted or grounded. Either way it could cause excess current through that brush for immature failure. Not sure how you polished the slip ring, buts its normally done with the genset at speed and excitation shut off. Either way if you have field pole part failures or exciter failure its time for a gen overhaul. Was it building voltage and holding load? Often slip ring/brush failures happen with high loads. I'd locate an Onan dealer when possible.
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Old 06-05-2012, 02:29 PM   #14
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I would notify dealer, take photos of two failed brushes. You make it sound as though its the same brush each time. If so that normally means the excitor feeding this brush for excitation of the and/or field poles is shorted or grounded. Either way it could cause excess current through that brush for immature failure. Not sure how you polished the slip ring, buts its normally done with the genset at speed and excitation shut off. Either way if you have field pole part failures or exciter failure its time for a gen overhaul. Was it building voltage and holding load? Often slip ring/brush failures happen with high loads. I'd locate an Onan dealer when possible.

These brushes are "signal" sensinf only, independent of load. They only sense phase and frequency, and are across a transformer secondary. The apparent cause of the problem is a bad slip ring. I have cleaned trhe slip rings, and am awaiting a new brush block. There was, I found yesterday, an arced spot on the upper slip ring. I used a chunk of Scotchbrite pad and polished it off (very tedious), and will see what happens.

Field pole parts don't require an overhaul, but if the slip ring is bad, I'll have a 1,000-hour service done while the genny is out!

We have a guy here that'll pull the generator at my house and take it to his shop for repairs.
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Old 06-05-2012, 03:45 PM   #15
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Kind of curious how many hours do you have on your Onan 5.5? I ask to see how reliable they are and for how long. I just did my first oild change as per manual after gen has run 20 hrs.

Do you use generic oil filters?
What weight oil? 15W40?
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Old 06-05-2012, 07:51 PM   #16
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[QUOTE=Freds342;205964]These brushes are "signal" sensinf only, independent of load. They only sense phase and frequency, and are across a transformer secondary.
Field pole parts don't require an overhaul, but if the slip ring is bad, I'll have a 1,000-hour service done while the genny is out!




Wow, just trying to help. First I was responsible for operation and repair of "generators" from 50 KW to 250KW emergency standby units. Turbine or diesel generator sets to 2500KW and propulsion gen sets up to 7000 HP.

I can safely say they all have slip rings which feed the fields for excitation. Without it you get no output voltage. In the case above output range anywhere from 450VAC to 2300VAC. I've seen field poles disintegrate from overspeed, litrally burn from shorted turns and trip off line instantly due to grounds in the winding to the poles. Obviously field poles can and do fail. If its only a partial failure it causes brushes to go bad.

Slip rings are normally polished by "stones" made for the purpose, using emery cloth or and grit paper only causes grit to become embedded in the face and making the problem worse. The instumentation you refer to is on the "Stator" or stationary AC portion of the machine. DC can cross transformers. The last page of your Cummins installation manual is a schmetic of the assembly. It clearly shows the dc fed slip rings controlled by a VR, the instumention leads are just below do not connect to the slip rings.

At less than 1000 hours its not normal for slip rings to eat brushes. I'd get warranty help if still available.

BTW commutators are only part of DC machines, not AC.
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Old 06-05-2012, 08:05 PM   #17
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We just had our 4000 in the shop two weeks ago for burnt up brushes and it ended up being a $1600 repair! The little black control box was bad and unfortunately when those go out there is nothing to tell your generator to stop running. When it went out it was basically telling the generator it wasn't producing enough voltage, which then caused the generator to run so hot we had to replace the bearings, the Armature, the brushes, the starter gear and the control board.

Not saying that's what's wrong with yours but that is the same code that was flashing when ours went out. So if it does it again it may be some deeper seeded problems.

I now have a voltage meter continuously plugged inside the camper. My brother-in-law and I are working on one that has an alarm that sounds when it goes high or low.
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Old 06-06-2012, 01:06 PM   #18
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Originally Posted by Iggy View Post
Fred
Kind of curious how many hours do you have on your Onan 5.5? I ask to see how reliable they are and for how long. I just did my first oild change as per manual after gen has run 20 hrs.

Do you use generic oil filters?
What weight oil? 15W40?
It currently has 840 hours on it. The first failure was at 720. I use 15W-40 Mobil1, and Wix filters.
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Old 06-06-2012, 01:24 PM   #19
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[QUOTE=VinceU;206124]
Quote:
Originally Posted by Freds342 View Post
These brushes are "signal" sensinf only, independent of load. They only sense phase and frequency, and are across a transformer secondary.
Field pole parts don't require an overhaul, but if the slip ring is bad, I'll have a 1,000-hour service done while the genny is out!




Wow, just trying to help. First I was responsible for operation and repair of "generators" from 50 KW to 250KW emergency standby units. Turbine or diesel generator sets to 2500KW and propulsion gen sets up to 7000 HP.

I can safely say they all have slip rings which feed the fields for excitation. Without it you get no output voltage. In the case above output range anywhere from 450VAC to 2300VAC. I've seen field poles disintegrate from overspeed, litrally burn from shorted turns and trip off line instantly due to grounds in the winding to the poles. Obviously field poles can and do fail. If its only a partial failure it causes brushes to go bad.

Slip rings are normally polished by "stones" made for the purpose, using emery cloth or and grit paper only causes grit to become embedded in the face and making the problem worse. The instumentation you refer to is on the "Stator" or stationary AC portion of the machine. DC can cross transformers. The last page of your Cummins installation manual is a schmetic of the assembly. It clearly shows the dc fed slip rings controlled by a VR, the instumention leads are just below do not connect to the slip rings.

At less than 1000 hours its not normal for slip rings to eat brushes. I'd get warranty help if still available.

BTW commutators are only part of DC machines, not AC.
Whup! You're right, The field current does vary with load, the quadrature winding of the stator is the sensing winding.

The dressing that I did was very light with 200 grit emery, and the ring looks clean everywhere I could get the rotor to stop.

What I meant by not needing an o'haul is that if the engine runs fine, why tear it down with only 840 hours? If it has to come out, I can see going ahead and doing the 1,000 hour service, but that's all.

The "Warranty" appears to only cover the engine wetted parts, the circuit board(s), and the "regulator", which might be argued. I'd say that the slip rings are part of the regulator, but they might say no.

What do you think?

And I appreciate the help!
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Old 06-07-2012, 09:15 AM   #20
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Based on conditions and shortened interval between failures it's time for a motor shop to inspect hopefully Onan due to electronic controls. Don't treat the result, find the cause. The problem can lie from the auto volt control to the field poles, short, ground or "bad iron", shorted laminations. Partial brush failure should not occur with hours so low. One thing for certain, machines operating at 3600 rpm often self destruct if something goes wrong. BTW the 5.5KW costs $7500 with discount, need to baby this unit. Good luck
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